Single port single connection VNA calibration apparatus

ABSTRACT

A method and apparatus are used to calibration a Vector Network Analyzer (VNA). The method includes providing a calibration module with a single port, providing within the calibration module a set of reflecting components with known scattering parameters, providing control signals to the calibration module through the single port, providing the known scattering parameters to the VNA through the single port, coupling one of reflecting components to the VNA, measuring scattering parameters, and comparing the measured scattering parameters with the known scattering parameters. The apparatus includes a calibration module and a controller module. In one embodiment, the calibration module includes a set of reflecting components, a memory that stores the characterization data, and a current source which sends characterization data in the form of current pulses to the controller module. The controller module includes a voltage source that generates the control signals used by the calibration module.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to calibration of vector networkanalyzers in general and in particular to a single port, singleconnection calibration apparatus.

[0003] 1. Description of the Related Art

[0004] Measurement errors in any vector network analyzer (VNA)contribute to the uncertainty of the device being measured by the VNA.By quantifying these errors, their effects can be drastically reduced.Measurement errors in network analysis can be separated into twocategories: random errors and systematic errors. Random errors arenon-repeatable measurement variations due to physical change (e.g.,noise and temperature changes) and, therefore, are usuallyunpredictable. Systematic errors are repeatable measurement variationsin the test setup itself (e.g., directivity, source match, frequencyresponse, and leakage).

[0005] In most measurements made on “devices under test” (DUT) with aVNA, the systematic errors are the most significant source ofmeasurement uncertainty. Therefore, it is desirable to remove theseerrors from the VNA measurements. This is achieved through a VNAcalibration.

[0006] The traditional calibration method requires an operator to pressa sequence of buttons on a VNA and manually connect and remove at leasethree “perfect” calibration components. The VNA measures each componentand transfers the accuracy of the standards to the VNA. This calibrationprocess is time-consuming and prone to operator error.

[0007] In contrast, an automatic calibration device is useful because itreduces calibration time and reduces the chance of operator error. Aprior art automatic calibration device for a one-port VNA is depicted inFIG. 1. The automatic calibration device 116 shown in FIG. 1 requires anoperator to connect the calibration device 116 to a test port 104 of theVNA 102 and press a button. The calibration device 116 thenautomatically calibrates the VNA by connecting the calibrationcomponents 120,122, and 124 to test port 106 through switch 118. Thecalibration device 116 does not require “perfect” calibrationcomponents. Imperfect calibration components 120, 122 and 124 can beused as long as their characteristics (S-parameters) are repeatable andaccurately measured. These S-parameters are stored for use by the VNA102. During calibration, the VNA 102 measures the three calibrationcomponents 120, 122 and 124, and these measurement results and thepreviously stored S-parameter data are used to calculate correctionfactors. Calibration component 126 is used for verifying the accuracy ofthe VNA after it has been calibrated.

[0008] With the automatic calibration device depicted in FIG. 1, twotypes of communication are performed between the calibration device 116and the VNA 102. The first type of communication includes thetransmission of digital control signals between the calibration deviceand the controller 128, while the second type of communication includesthe transmission and reception of microwave/radio (RF) signals betweenthe calibration device and the VNA. Thus, communication between thecalibration device 116 and the VNA 102 requires at least two ports onboth the calibration device and the VNA, along with two separate cables.A first cable 114 carries the digital control signals between a firstset of ports (108, 110), while a second cable 112 carries the RF signalsthrough a second set of ports (104, 106). In addition, the calibrationdevice 116 requires an external power supply.

[0009] Accordingly, it is an object of the present invention to providea method and apparatus for calibrating a VNA that requires only onecable and one set of ports for communication between an automaticcalibration device and the VNA. It is a further object of the presentinvention that the calibration device draw its power from the singlecable.

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, an apparatus and methodfor calibrating a VNA are provided. The method in accordance with thepresent invention includes the steps of providing a calibration modulewith a single port, providing within the calibration module a set ofreflecting components with known scattering parameters, providingcontrol signals to the calibration module through the single port,providing the known scattering parameters to the VNA through the singleport, coupling one of reflecting components to the VNA, measuringscattering parameters, comparing the measured scattering parameters withthe known scattering parameters, and determining calibration valueswhich can be utilized to correct errors introduced by the VNA. Thereflecting components include a short, an open and a low reflectionimpedance. The VNA transmits control signals to the calibration moduleby transmitting at least three voltage levels to the calibration module.The calibration module transmits the known scattering parameters to theVNA by transmitting current pulses to the VNA.

[0011] One implementation of an apparatus to calibrate a VNA using themethod described includes a calibration module and a controller module.The calibration module includes a set of reflecting components and aswitch for connecting the reflecting components. The switch iscontrolled by control signals received from the controller module. Thecalibration module further includes a memory for storing the knownscattering parameters for the reflecting components and amicrocontroller coupled to the memory. In alternate embodiments, thememory can also store the date when the scattering parameters for thereflecting components were stored and the ambient temperature at whichthe scattering parameters were stored. The microcontroller is controlledby the control signals received from the controller module. Alsoincluded in the calibration module is a current source coupled to themicrocontroller, wherein the current source provides current pulses tothe controller module under direction of the microcontroller. Thecontroller module includes a processor, a voltage source coupled to theprocessor, wherein the voltage source, under direction of the processor,generates the control signals used by the calibration module. Thecontroller module further includes a convertor coupled to the processor,wherein the convertor receives the current pulses from the currentsource of the calibration module, and wherein the convertor converts thecurrent pulses into voltage levels to be used by the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Details of the present invention will appear more clearly fromthe following description in which the preferred embodiment of theinvention has been set forth in conjunction with the drawings in which:

[0013]FIG. 1 is a block diagram depicting a prior art automatic VNAcalibration device;

[0014]FIG. 2 is a block diagram of a VNA calibration apparatus inaccordance with the present invention;

[0015]FIG. 3 is a block diagram of a calibration module in accordancewith the present invention;

[0016]FIG. 4 is a block diagram of a controller module in accordancewith the present invention;

[0017]FIG. 5 is a schematic diagram of a portion of a calibration modulein accordance with the present invention;

[0018]FIG. 6A is a schematic diagram of a portion of a calibrationmodule in accordance with the present invention;

[0019]FIG. 6B is a waveform diagram depicted in conjunction with FIG.6A;

[0020]FIG. 7 is a schematic diagram of a portion of a controller modulein accordance with the present invention;

[0021]FIG. 8 is a schematic diagram of a portion of a controller modulein accordance with the present invention;

[0022]FIG. 9A is a schematic diagram of a portion of a controller modulein accordance with the present invention; and

[0023]FIG. 9B is a waveform diagram depicted in conjunction with FIG.9A.

DETAILED DESCRIPTION

[0024]FIG. 2 depicts a general overview of a VNA calibration apparatusin accordance with the present invention. As shown in FIG. 2, VNA 400and calibration module 300 communicate through a single RF line 202,which couples RF port 402 with RF port 302. RF line 202 carries controlsignals from VNA 400 to calibration module 300, and carries data fromcalibration module 300 to VNA 400. Controller module 410, which in oneembodiment is housed inside VNA 400, is connected to RF port 402. Switchassembly 304 couples the reflecting components 306, 308, 310, and 312 toRF port 302.

[0025] The manner of communication between VNA 400 and calibrationmodule 300 will now be discussed. Controller module 410transmits controlsignals to calibration module 300 through RF line 202. These controlsignals control the position of switch assembly 304 and the functions ofmicrocontroller 314. Controller module 410 controls the operation ofswitch assembly 304 by placing four distinct DC voltage levels on RFline 202. Each voltage level causes switch assembly 304 to connect oneof the reflecting components 306, 308, and 310, or verificationcomponent 312, to RF port 302. Controller module 410 controls thefunctions of microcontroller 314 by toggling between two DC voltagelevels on RF line 202. Calibration module 300 senses the edges of thepulses and converts the edges into logic level signals for use bymicrocontroller 314.

[0026] Calibration module 300 transmits stored characterization data(S-parameters) for the reflecting components to VNA 400 by varying thecurrent on RF line 202. VNA 400 senses the current on RF line 202 andconverts the current pulses into logic level signals for use by theVNA's microprocessor (not shown in FIG. 2). Additionally, calibrationmodule 300 is powered by DC voltage transmitted through RF line 202.

[0027]FIG. 3 is a block diagram depicting details of calibration module300. RF port 302 of calibration module 300 is connected to RF port 402of VNA4 00. Calibration module 300 includes switch assembly 304 havingat least four positions for coupling reflecting components 306, 308, and310, and verifying component 312, to RF port 302. (The reflectingcomponents are referred to collectively with reference number 334.) Ingeneral, while more than three reflecting components could be used forcalibration, only three are necessary so long as their respectiveS-parameters are known and sufficiently distinct from each other.

[0028] Switch assembly 304 is controlled by voltage sense 318. Voltagesense 318, along with the remaining components of calibration module300, receive DC signals from RF port 302 through RF choke 316. RF choke316 isolates microwave/RF signals from voltage sense 318. Voltage sense318 senses the four voltage levels sent as control signals through RFport 302 and causes switch assembly 304 to make the appropriateconnections based upon these voltage levels.

[0029] Power regulator 320 provides a constant 5V DC power source forvarious components of calibration module 300, including pulse edgedetector 322, comparator 324, microcontroller 314, memory 326, andtemperature sensor 328. The DC power is drawn directly from the DCvoltage on RF port 302.

[0030] Memory 326 stores characterization data for the reflectingcomponents. This information is recalled and transmitted to VNA 400under the direction of microcontroller 314. Microcontroller 314, inturn, operates under the direction of control signals received fromcontroller module 410 through RF port 302. Controller module 410transmits these control signals by toggling RF port 302 between two DCvoltage levels. Pulse edge detector 322 senses the edges of the pulses,while comparator 324 converts the edges into logic level signals for useby microcontroller 314. In an alternate embodiment, the memory 326 canalso store a date when the scattering parameters for the reflectingcomponents were stored and the ambient temperature at which thescattering parameters were stored in memory 326. The storage date andtemperature can be accessed to determine the when the module'sreflecting components were last characterized. In one embodiment, themodule's reflecting components are re-characterized on an annual basisto mitigate the effects of aging. However, in alternate embodiments themodule's reflecting components can be re-characterized more or lessfrequently.

[0031] Calibration module 300 transmits the stored characterization datato VNA 400 by varying the current on RF port 302. This varied current isgenerated by constant current source 332. The operation of constantcurrent source 332 is controlled by microcontroller 314. Calibrationmodule 300 optionally contains a temperature sensor 328. Becausecharacterization data can be affected by temperature, temperature sensor328 provides the ability to measure the temperature at the time thereflecting components are characterized. This temperature is stored inmemory 326 for future reference.

[0032]FIG. 4 is a block diagram depicting details of controller module410. Controller module 410 is coupled to the VNA microprocessor 420through switch assembly 418. When controller module 410 is not in use,microprocessor 420 is coupled to the VNA's serial port. Controllermodule 410 receives DC signals from RF port 402 through RF choke 404. RFchoke 404 ensures that RF signals do not enter into the controllermodule. DC relay 406 couples RF choke 404 to the remainder of controller410.

[0033] Voltage source 416, under the direction of microprocessor 420,provides the DC voltage levels that operate as control signals forcalibration module 300. As explained above, controller module 410controls switch assembly 304 by placing four distinct voltage levels onRF port 402, and controls microcontroller 314 by toggling between twovoltage levels on RF port 402. Additionally, controller module 410receives characterization data from calibration module 300 through RFport 402. As explained above, calibration module 300 transmits thecharacterization data by varying the current on RF port 402. Current tovoltage convertor 408 measures the current levels by measuring thevoltage across resistor 414, and converts these current levels intovoltage levels. Pulse shaper amplifier 411 and comparator 412 thenconvert these voltage levels into logic level signals that can be usedby VNA microprocessor 420.

Calibration Module

[0034] Further details of calibration module 300 will now be discussed.FIGS. 5 and 6 together provide a schematic diagram of one embodiment ofcalibration module 300 in accordance with the present invention. FIG. 5depicts RF choke 316, switch assembly 304, voltage sense 318, andreflecting component 334. FIG. 6A depicts pulse edge detector 322,comparator 324, microcontroller 314, memory 326, temperature sensor 328and constant current source 332. FIGS. 5 and 6A are connected at points“1” and “2.” Each component depicted the accompanying figures is labeledwith an example component value. Resistor values are represented inohms, capacitor values in farads, and inductor values in henries,wherein “K” represents kilo-, “U” represents micro-, and “N” representsnano-. It should be noted that several components in the figures (e.g.,resistors and capacitors) can be combined into a single component ofequivalent value.

[0035] With reference to FIG. 5, voltage sense 318 senses the four DCvoltage levels sent as control signals through RF port 302 and causesswitch assembly 304 to make the appropriate connections based upon thesevoltage levels. In one embodiment, a voltage level greater than −7.1Vconnects RF port 302 to an “open” component, a voltage between −7.1V and−11.6V connects RF port 302 to a “short,” and a voltage less than −11.6Vconnects RF port 302 to a “match.” Voltage sense 318 receives these DCvoltage levels through RF choke 316.

[0036] The operation of voltage sense 318, switch assembly 304 andreflecting component 334 will now be discussed in the context ofswitching to an “open” component. Controller module 410 places a DCvoltage level greater than −7.1V on RF port 302 (+9V in this example).This potential on Node B turns off diodes CR3, CR4 and CR5, causingreflecting component 334 to behave like an open circuit.

[0037] The operation of voltage sense 318, switch assembly 304 andreflecting component 334 will now be discussed in the context ofswitching to a “short” component. Controller module 410 places a DCvoltage level between −7.1V and −11.6V on RF port 302 (−10V in thisexample). A voltage of −10V on RF port 302 drives diodes CR2 and CR3,and the gates of transistors Q2-Q7. With transistor Q2 turned on, thepotential on the gate of transistor Q4 is lowered to ground, thusturning off transistor Q4. The potential on the gates of transistors Q5and Q7 is also lowered to ground through Q3, turning off transistor Q5and Q7. With transistors Q4 and Q5 both turned off, a negative potentialremains on the gate of transistor Q6, turning on transistor Q6 andproviding a DC connection to ground for diode CR4. Together with thenegative potential applied to Node B, such a configuration turns ondiode CR4 and turns off diode CR5. With CR4 on, the capacitors C4 and C5provide a low impedance path to ground for RF signals at the test port.Hence, reflecting component 334 behaves like an short circuit.

[0038] Lastly, the operation of voltage sense 318, switch assembly 304and reflecting component 334 will now be discussed in the context ofswitching to a “match” (or “load”) component. Controller module410places a DC voltage less than −11.6V on RF port 302 (−15V in thisexample). A voltage of −15V on RF port 302 drives diodes CR1, CR2 andCR3, and the gates of transistors Q1-Q7. With transistors Q1 and Q2turned on, the potential on the gates of transistors Q3 and Q4 islowered to ground, turning off transistors Q3 and Q4. Transistors Q5 andQ7 remain on because their gate potential remains negative. Withtransistor Q5 turned on, the gate potential of transistor Q6 is loweredto ground, turning off transistor Q6. Together with the negativepotential applied to Node B, such a configuration turns on diode CR5 andturns off diode CR4. With CR5 on, capacitors C6 and C7 and resistor R14provide a nearly resistive impedance to ground for RF signals at thetest port. Thus, reflecting component 334 behaves like a “match” or“load.”

[0039]FIG. 5 also comprises power regulator 320. Power regulator 320receives DC voltage from RF port 302 through RF choke 316, and providesa constant 5V voltage source for various components of calibrationmodule 300, including pulse edge detector 322, comparator 324,microcontroller 314, memory 326, and temperature sensor 328. Powerregulator 320 comprises component U1 which converts an input voltageinto a 5V output voltage. In one embodiment, component U1 comprisesLinear Technology part no. LT1761ES5.

[0040] Attention is now drawn to FIG. 6A. As discussed above,microcontroller 314 operates under the direction of control signalsreceived from controller module 410 through RF port 302. Controllermodule 410 transmits these control signals by toggling RF port 302between two DC voltage levels. In one embodiment, RF port 302 is toggledbetween 9V and 11V. Pulse edge detector 322 senses the edges of thepulses, while comparator 324 converts the edges into logic level signals(0V to 5V) for use by microcontroller 314.

[0041] The operation of pulse edge detector 322 and comparator 324 willnow be discussed. Controller module 410 toggles the voltage on RF port302 between 9V and 11V. The RF port's voltage waveform appears as asquare wave, as shown in FIG. 6B. Resistor R19 and capacitor C15 form adifferentiator. Current flows through R19 and C15 only during thetransitions between 9V and 11V. The current decays to zero after thetransition. Since Node C is nominally at 2.5V, which is set by the 5Vsource and resistors R20 and R21, the current flow through R19 and C15will perturb Node C's voltage when the input signal transitions between9V and 11V, as shown in FIG. 6B. Comparator 324 compares the voltage atNode C with the voltage at Node E. If the voltage on Node C is greaterthan the voltage on Node E, the output of comparator 324 changes to 0V.Thus, Node E's voltage sets the threshold voltage for the comparator tochange state.

[0042] Comparator 324 has two thresholds set by resistors R23, R24 andR25 and the state of the comparator's output. When the comparator'soutput is 5V, the voltage on Node E equals 2.9V, and when thecomparator's output is 0V, the voltage on Node E equals 2.1V. Having twothresholds reduces the chance of the comparator switching states due tonoise on the input waveform. This is a common technique called“hysteresis.” Diodes CR6 and CR7 act as limiters. They prevent Node Cfrom rising above +5.3V or falling below −0.3V.

[0043] The waveforms depicted in FIG. 6B will now be discussed in moredetail in conjunction with FIG. 6A. Initially, the voltage on RF port302 is constant at 9V and Node C is at 2.5V. Assuming the output ofcomparator 324 to be 5V, Node E is at 2.9V. (Upon powering upcalibration module 300, the output of comparator 324 maybe either 5V or0V, but by applying an initialization pulse sequence, the comparator'soutput can be set to 5V before data transmission from the VNA 400 tocalibration module 300). Next, the voltage on RF port 302 changes from9V to 11V. This causes current to flow through R19 and C15 during thetransition and perturbs Node C's voltage. Node C jumps from 2.5V to 3.3Vand decays back to 2.5V as the current flow through R19 and C15diminishes to zero. Since Node C's peak voltage (3.3V) is greater thanNode E (2.9V), the comparator 324's output will change from 5V to 0V.After the comparator's output changes to 0V, the voltage on Node E willthen become 2.1V. This sets the new threshold for comparator 324 tochange its output state.

[0044] Next, the voltage on RF port 302 changes from 11V to 9V. Again,current flows through R19 and C15 during the transition and perturbsNode C's voltage. The direction of current flow causes Node C to jumpfrom 2.5V to 1.7V. As current flow through R19 and C15 diminishes, NodeC recovers to 2.5V. Since Node C's minimum voltage (1.7V) is less thanNode E (2.1V), the output of comparator 324 will change from 0V to 5V.

[0045] Memory 326 depicted in FIG. 6A stores characterization data forthe reflecting components. In one embodiment, memory 326 comprises Atmelpart no. AT25256W-10SC-2.7. This characterization data is recalled andtransmitted to VNA 400 under the direction of microcontroller 314,which, in turn, operates under the direction of control signals receivedfrom controller module 410. In one embodiment, microcontroller 314comprises National Semiconductor part no. COP8SAA716M8P. The storedcharacterization data is transmitted to VNA 400 by varying the currenton RF port 302. This varied current is generated by constant currentsource 332, which includes switch (transistor) Q8. Transistor Q8 iscontrolled by microcontroller 314.

[0046] As shown in FIG. 6A, calibration module 300 contains atemperature sensor 328. Because characterization data can be affected bytemperature, temperature sensor 328 provides the ability to measure thetemperature at the time the reflecting components are characterized.This temperature is stored in memory 326 for future reference. In oneembodiment, temperature sensor 328 comprises Analog Devices part no.AD7814ART.

Controller Module

[0047] Further details of controller 410 will now be discussed. FIGS. 7,8 and 9A together provide a schematic diagram of one embodiment ofcontroller module 410 in accordance with the present invention. FIG. 7depicts voltage source 416, FIG. 8 depicts current to voltage convertor408, and FIG. 9A depicts pulse shaper amplifier 411 and comparator 412.The figures are connected at points “1” and “2.”

[0048] With reference to FIG. 7, voltage source 416 consists of anop-amp U1 that generates the four DC voltage levels sent as controlsignals to calibration module 300. In one embodiment, the four voltagelevels that are generated are −10V, −15V, +9V and +11V. The desiredvoltage is selected by switching the right combination of resistors andvoltages to the op-amp inputs.

[0049] With reference to FIG. 8, current to voltage convertor 408measures the current drawn from calibration module 300 by measuring thevoltage across resistor R1 (resistor 414 of FIG. 4). Instrumentationamplifier U1 then amplifies this voltage drop. In one embodiment,amplifier U1 comprises Texas Instruments part no. INA145UA. The outputof current to voltage convertor 408 is fed into pulse shaper amplifier411 and brought up to suitable DC values for input into comparator 412.Comparator 412 converts these voltage levels into logic level signalsthat can be used by VNA microprocessor 420.

[0050] Lastly, with reference to FIG. 9A and 9B, pulse shaper amplifier411 comprises two sections: the amplifier built around U1 and a servo(or“zeroing”) circuit built around U2. The calibration module 300modulates the current to send data to controller module 410. In oneembodiment, the current is toggled between 3 mA and 13 mA. Current tovoltage converter 408 converts the current to a voltage signal. As shownin FIG. 9B, the voltage signal received in this embodiment from currentto voltage converter 408 (at Node A) looks like a square wave withamplitude=511 mV and a DC offset=153 mV.

[0051] The signal on Node A is fed into amplifier U1, which hasgain=(−R2/R1) =−2. Diodes CR2-CR4 limit the minimum output level=−0.9Vand diode CR1 limits the maximum level=+0.5V. Since the input signal hasa DC offset, U1 amplifies it causing the output to also have a DCoffset. One way to remove the DC offset is to use a servo circuit thatforces the DC offset at the output of U1 to be 0V. Q1 is a switch thatconnects U1's output to the input U2. U2 acts as an integrator. U2'soutput is scaled down by R9 and R10 and connected to the positive inputof U1. The circuit monitors U1's output level and sends a correctionvoltage to U1's positive input, causing the output of U1 to be 0V. Theservo's input needs to be disconnected from U1's output after its outputhas been “zeroed.” Otherwise, U1 remains at 0V even when there is asquare wave at Node A. Once disconnected, the servo circuit can stillhold U1's output to 0V until node A's voltage changes. When receivingdata from the calibration module 300, U1's output (after being zeroed)appears as a square wave toggling between 0V and −0.9V. Resistors R11and R12 serve as a level shifter and shift U1's output to 1V and 1.8V.See FIG. 9B. This signal is then connected to the input of comparator412. Comparator 412 has threshold voltages of 1.25V and 1.45V. Thethresholds are set by resistors R13, R14, R15, R16, and the state of thecomparator's output.

[0052] The foregoing detailed description of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. The described embodiments were chosen inorder to best explain the principles of the invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the claims appended hereto.

What is claimed is:
 1. An apparatus for use in calibrating a Vector Network Analyzer, the apparatus comprising: a port; a set of reflecting components providing a set of known scattering parameters; a microcontroller operatively coupled to the port and the memory; and a current source operatively coupled to the microcontroller and the port, wherein the microcontroller is configured for providing the set of known scattering parameters by way of current pulses from the current source.
 2. The apparatus of claim 1, further comprising a pulse edge detector operatively coupled to the port and a comparator operatively coupled to the pulse edge detector and the microcontroller, wherein the microcontroller is configured for receiving control signals from the port that are detected by the pulse edge detector and providing the set of known scattering parameters in response to the control signals.
 3. The apparatus of claim 2, wherein the control signals comprise at least two voltage levels.
 4. The apparatus of claim 1, further comprising a memory operatively coupled to the port and the microcontroller, wherein the memory stores the set of known scattering parameters.
 5. The apparatus of claim 4, further comprising a power regulator operatively coupled to the port and the microcontroller and the memory.
 6. The apparatus of claim 1, wherein the set of reflection components comprises a short, an open and a low reflection impedance.
 7. An apparatus for use in calibrating a Vector Network Analyzer (VNA), the apparatus comprising: a port; a set of reflecting components providing a set of known scattering parameters; a switch having a first end operatively coupled to the port and a second end selectively connectable to individual ones of the set of reflection components, wherein the switch is controlled by a first set of control signals received through the port; a microcontroller operatively coupled to the port, wherein the microcontroller is controlled by a second set of control signals received through the port; and a current source operatively coupled to the microcontroller and the port, wherein the current source provides current pulses through the port under direction of the microcontroller.
 8. The apparatus of claim 7, further comprising a memory operatively coupled to the port and the microcontroller, wherein the memory stores the set of known scattering parameters.
 9. The apparatus of claim 8, further comprising power regulator operatively coupled to the port and the microcontroller and the memory.
 10. The apparatus of claim 7, further comprising a voltage sensor operatively coupled to the port and the switch, wherein the voltage sensor is configured for receiving the first set of control signals and for controlling the operation of the switch.
 11. The apparatus of claim 7, wherein the set of reflection components comprises a short, an open and a low reflection impedance.
 12. The apparatus of claim 7, wherein the first set of control signals comprises at least three voltage levels.
 13. The apparatus of claim 7, wherein the second set of control signals comprises at least two voltage levels.
 14. An apparatus for use in calibrating a Vector Network Analyzer, the apparatus comprising: a port; a processor; a voltage source operatively coupled to the processor and the port; and a current to voltage convertor operatively coupled to the port and the processor.
 15. The apparatus of claim 14, further comprising a switch having a first end operatively coupled to the processor and a second end selectively connectable to the port.
 16. The apparatus of claim 14, further comprising a pulse shaper amplifier and a comparator, wherein the pulse shaper amplifier is operatively coupled to the current to voltage convertor and the comparator, and wherein the comparator is operatively coupled to the pulse shaper amplifier and the processor.
 17. An apparatus for use in calibrating a Vector Network Analyzer, the apparatus comprising: a port; a processor; a voltage source operatively coupled to the processor and the port, wherein the voltage source, under direction of the processor, generates control signals to be transmitted through the port; and a convertor operatively coupled to the processor and the port, wherein the convertor receives current pulses through the port, and wherein the convertor converts the current pulses into voltage levels to be used by the processor.
 18. An apparatus for use in calibrating a Vector Network Analyzer (VNA), the VNA having a first port, the apparatus comprising: a calibration module comprising: a second port for connecting to the first port; a set of reflecting components providing a set of known scattering parameters which enable calculation of calibration values used to correct errors introduced by the VNA; a switch having a first end operatively coupled to the second port and a second end selectively connectable to individual ones of the set of reflection components, wherein the switch is controlled by a first set of control signals received through the second port; a memory for storing the set of known scattering parameters; a microcontroller operatively coupled to the memory and the second port, wherein the microcontroller is controlled by a second set of control signals received through the second port; and a current source operatively coupled to the microcontroller and the second port, wherein the current source provides current pulses through the second port under direction of the microcontroller; and a controller module comprising: the first port; a processor; a voltage source operatively coupled to the processor and the first port, wherein the voltage source, under direction of the processor, generates the first and second sets of control signals used by the calibration module; and a convertor operatively coupled to the processor and the first port, wherein the convertor receives the current pulses from the current source of the calibration module, and wherein the convertor converts the current pulses into voltage levels to be used by the processor.
 19. The calibration apparatus of claim 18, wherein the set of reflection components comprises a short, an open and a low reflection impedance.
 20. The calibration apparatus of claim 18, wherein the microcontroller provides the set of known scattering parameters to the processor by way of the current pulses, and wherein the processor determines the calibration values by comparing the set of known scattering parameters to measured scattering parameters.
 21. The calibration apparatus of claim 18, wherein the first set of control signals comprises at least three voltage levels.
 22. The calibration apparatus of claim 18, wherein the second set of control signals comprises at least two voltage levels.
 23. The calibration apparatus of claim 18, wherein the calibration module is powered by voltage received through the second port.
 24. The calibration apparatus of claim 18 wherein the calibration module further comprises a temperature sensor.
 25. A method of calibrating a Vector Network Analyzer (VNA), the VNA having a first port, the method comprising the steps of: providing a calibration module with a second port for connecting to the first port; providing within the calibration module a set of reflecting components providing known scattering parameters; providing control signals to the calibration module through the first port; providing the known scattering parameters to the VNA through the second port; coupling one of the set of reflecting components to the second port; measuring scattering parameters after the above coupling step; comparing the measured scattering parameters with the known scattering parameters; and determining calibration values which can be utilized to correct errors introduced by the VNA.
 26. The method of claim 25, wherein the step of providing control signals to the calibration module through the first port further comprises providing at least three voltage levels.
 27. The method of claim 25, wherein the step of providing the known scattering parameters to the VNA through the second port further comprises providing current pulses.
 28. The method of claim 25, wherein the step of providing within the calibration module a set of reflecting components comprises providing a short, an open and a low reflection impedance.
 29. A method for communicating between a Vector Network Analyzer (VNA) and a calibration apparatus comprising a set of reflecting components providing a set of known scattering parameters, the method comprising the steps of: providing control signals from the VNA to the calibration apparatus by transmitting at least three voltage levels to the calibration apparatus; and providing the set of known scattering parameters from the calibration apparatus to the VNA by transmitting current pulses to the VNA.
 30. A method for providing control signals to a Vector Network Analyzer calibration apparatus comprising a port and a set of reflecting components providing a set of known scattering parameters, the method comprising the steps of: providing a processor; providing a voltage source operatively coupled to the processor and the port; and generating on the port at least three voltage levels from the voltage source under direction of the processor.
 31. A method for providing to a Vector Network Analyzer (VNA) a set of known scattering parameters for a set of reflecting components, the method comprising the steps of: providing a memory for storing the set of known scattering parameters; providing a microcontroller operatively coupled to the memory; providing a current source operatively coupled to the microcontroller; and transmitting current pulses from the current source to the VNA under direction of the microcontroller. 